SKULL AND VISCERAL SKELETON OF THE GREENLAND SHARK. 303 



front, but widely separated behind. The anterior ends of the cartilages are only in con- 

 tact with each other for a short distance, and below this point of contact an elliptical 

 piece of cartilage, the basi-mandibular (PL I. Fig. 2, Bm), lies between them. The 

 mandibular cartilages, which are wide at the symphysis, increase in width as they pass out- 

 wards and backwards. Internally, at the hinder part of each cartilage, a rounded process 

 projects backwards and inwards. In the recent state, a ligament, in which an interarti- 

 cular cartilage lies imbedded, connects this with the suspensorial process of the cerato- 

 hyal cartilage. On the upper surface of the rounded process just described there is an 

 articular process which abuts against a similar surface on the upper jaw. External to 

 the process there is a concavity on which the articular process at the posterior end of 

 the palato-pterygoid rests. 



Teeth are found along the upper edge and inner surface of each mandibular cartilage 

 in its anterior two-thirds. A narrow shelf of cartilage lies along the lower part of the 

 dentigerous surface, and above this shelf the youngest teeth are situated. 



Labial Cartilages (PL I. Fig. 2, PL II. Fig. 1, L 1/ L"). — These stand in relation to 

 the upper and lower jaws. There are three cartilages on each side, and of the three, two 

 (L I/) stand in relation to a palato-pterygoid cartilage, while the third (L") lies in relation 

 to a mandibular cartilage. The two upper cartilages lie across the palato- quadrate cartilage 

 about the middle of its extent. One of them (L/) is an elongated, curved, cylindrical rod, 

 which has a direction from above downwards and backwards, and its lower extremity is 

 connected with a similar rod of cartilage (L") which is connected with the mandibular 

 cartilage. The other upper labial cartilage (L), which is flattened, is shorter than the 

 one just described, and lies across its upper extremity, and is superficial to it. The labial 

 (L") of the lower mandibular cartilage resembles the rod-like cartilage of the palato- 

 pterygoid. It has a direction from below upwards and backwards. Its upper extremity 

 is bound to the upper rod-like cartilage by connective tissue, and the two meet each other 

 at the angle of the mouth. 



The Cartilage of the Skull and Visceral Skeleton. 



The cartilage of which these are composed is soft as in Hexanchus, and yields readily 

 to the scalpel. Only in a few parts does it show any indication of becoming calcified. 



Points of Special Interest 



The points which I consider of special interest in the skull and visceral skeleton are 

 the following: — (1) the cranio-vertebral connection; (2) the presence of an hypophysis 

 canal ; (3) the presence of a basi-mandibular cartilage ; (4) the presence of a hypo-hyal 

 cartilage at the fore and upper part of each cerato-basi-hyal joint ; (5) the large 

 number of basi-branchial cartilages, Laemargus possessing more of these than are found 

 in any other Elasmobranch yet described ; (6) the soft nature of the cartilage of the 

 cranium and visceral skeleton. 



VOL. XXXVII. PART II. (NO. 15). 2 X 



